Flux-weighted centroids are computed for every target and cadence in the PA component of the Pipeline [1]}, [2]}. These identify the photocenter of the target within its centroid aperture in every Kepler image frame. Target centroid positions vary with time due to systematic effects discussed earlier. Centroid positions also vary as a result of changes in stellar brightness associated with transiting planets and eclipsing binaries. There is no centroid motion in principle for foreground transiting planets and eclipsing binaries when aperture crowding is negligible and the background is perfectly removed. In practice, however, all apertures are crowded to some degree and background removal is imperfect. Hence, centroids shift during transit or eclipse to a measurable extent in many cases. Whether or not the motion is statistically significant must be ascertained.
